Assessment of Water Availability in the Sokoto Rima River ...article.sapub.org/pdf/10.5923.j.re.20140405.03.pdf · Resources and Environment 2014, 4(5): 220-233 DOI: 10.5923/j.re.20140405.03

Resources and Environment 2014, 4(5): 220-233

DOI: 10.5923/j.re.20140405.03

Assessment of Water Availability in the Sokoto Rima

River Basin

Abdullahi S. A.1,*

, Muhammad M. M.1, Adeogun B. K.

1, I. U. Mohammed

2

1Department of Water Resources and Environmental Engineering, Faculty of Engineering, Ahmadu Bello University, Zaria, Nigeria 2Department of Water Supply and Sanitation, National Water Resources Institute, Kaduna, Nigeria

Abstract The Sokoto-Rima River basin is located in the north western part of Nigeria, which comprise of four (4) states

(i.e Sokoto, Kebbi, Katsina and Zamfara) and have population of more than 15million according to 2006 census. This makes

the rivers and streams within the basin to be very important source of fresh water to the people living in those states.

Therefore, even small decrease in runoff within the basin could have dramatic effects on the water supply of the region. This

paper assesses and evaluates the impact of climate change on water availability and investigates the sensitivity of the basin to

climate change in Sokoto-Rima river basin using the Water Evaluation and Planning (WEAP) model. This model allows the

simulation and analysis of various water allocations and scenarios. The hydrological processes that occur for the six major

rivers within the basin during 1970 to 2013 was satisfactorily model and calibrated by visual observation and compared with

the measured data. The calibration process of the model was done using the first twenty two years climatological records

(1970-1992) and validated with the remaining data (1993-2013). Simulations are proposed for various climatic situations

considering the global climatic models (GCM) predictions. Six (6) developed climate change scenarios of temperature

increase (0, +0.5, +1℃) coupled with decrease or increases in precipitation (0,-10%, +10%) were combined and applied for

the study area in the WEAP model for simulation. Then, the climatically affected runoff, evapotranspiration, and water

demand series were obtained as output of the WEAP model. Results indicate that climate change will significantly reduce the

runoff, and increase evapotranspiration and water demand in the basin, more especially the demand for irrigation. The results

indicate an annual reduction in the total available water of about 1.70 billion cubic meter and monthly water demand of 17.11

Billion Cubic Meter for the month of April (which is the driest month in the basin) for the selected sites under 10% reduction

in the actual rainfall within the basin and increase in evapotranspiration under 1℃ increase in temperature, this indicate

reduction of the surface water in the future for the basin. In addition, the dependency of the basin on surface water sources

make it imperative to apply some methods of efficient use of water resources in the basin to ensure future sustainability. To

adapt to the current trend and minimize the significant impact on availability of water supply in the basin in the foreseeable

future, some proposed adaptation and mitigation measures to remedy this trend of scarcity ranges from sustainable

developments to collaborative planning among the stakeholders within the basin.

Keywords Climate, River basin, Availability and planning

1. Introduction

Climate in a narrow sense is usually defined as the average

weather, or more rigorously, as the statistical description in

terms of the mean and variability of relevant quantities over a

period of time ranging from months to thousands or millions

of years. The classical period for averaging these variables is

30 years, as defined by the World Meteorological

Organization. The intergovernmental panel on climate

change (IPCC) developed the variation of the earth

temperature for the past 140 years.

As climatic variability intensifies, changes in atmospheric

* Corresponding author:

[email protected] (Abdullahi S. A.)

Published online at http://journal.sapub.org/re

Copyright © 2014 Scientific & Academic Publishing. All Rights Reserved

conditions have altered water resources, their distribution in

space and time, the hydrological cycle of water bodies, water

quantity and, in more recent time, water supply systems and

requirements for water resources in the Sokoto-Rima river

basin, creating serious water shortages for household needs,

agriculture and industry.

With further significant variations in the climate of the

Sahel being predicted by General Circulation Models

(GCMs) (IPCC, 2007), it is important that scientific studies

be undertaken at regional levels so as to provide society with

accurate information on the real and potential impacts of

climate change, as well as, the mitigation and adaptation

options available. (Ekpoh and Ekpenyong, 2011).

The Sokoto-Rima River basin is located at north western

part of Nigeria and it covers four (4) states (i.e Sokoto, Kebbi,

Katsina and Zamfara) that have ninety two (92) local

government areas for administrative purpose. This makes the

Resources and Environment 2014, 4(5): 220-233 221

rivers and streams within the basin to be the important source

of surface water to the people living in those states.

Therefore, even small decrease in runoff within the basin

could have dramatic effects on the water supply of the

region.

To address this need, this study evaluates the impact of

climate change on available water resources in the six main

rivers of the Sokoto-Rima river basin using a decision

support system known as the Water Evaluation and Planning

(WEAP) Model. WEAP is an analytical framework

developed for the evaluation of climate change and other

drivers that water managers commonly confront (Yates et. al.,

2006). Indeed, WEAP model is one of the useful tools for the

integrated water resources management and it can be used as

a database for the forecasting and also as a policy analysis

tool, depending on the focus of the study. In this regard, the

applicability of WEAP in assessing the impact of climate

change as well as its main function of the sophisticated water

allocation model is tested in this study.

2. Statement of the Problem

According to Ringiuset, et. al. (1996) although climate

change is expected to affect many sectors of the natural and

man-made environment, water is considered to be the most

critical factor associated with climate impacts. A similar idea

is also highlighted by Houghton (1997) who stated that the

most important impact of global warming is on water

supplies which are in any case becoming increasingly critical

in many places. In the continent of Africa, the observational

records show that the climate has been warming through the

20th century at the rate of about 0.05°C per decade (IPCC,

2001).

In contrast to the assessment of global or large scale

variations of the climate driving forces for global hydrology,

the impact of climate change on the regional hydrology is

still unknown for most regions of the world (Kim et. al.,

2006). Although climate change is a global phenomenon, the

trends and impact may be different on a local scale.

2.1. Aims and Objectives of the Study

The aim is to analyse how sensitive is the Sokoto-Rima

River basin to climatic change with regards to its water

availability by developing a Model of the basin using WEAP,

and propose some mitigation measures that can minimize the

negative impact within the basin by the principle of mass

balance of the hydrologic quantity of the whole area.

While the objectives are:

i) To analyse the present situation of Sokoto-Rima River

Basin in order to evaluate the present hydrological

condition of the entire basin.

ii) To measure water availability and demand for each

sub-basin within the entire River Basin by considering

watershed characteristics and the demographic trends.

iii) To develop water resources WEAP model for the

Sokoto-Rima river basin in order to evaluate the impact

of climate change for current and future water

availability using water balance concept.

iv) To produce a simulation of the projected water

availability and to compare the water availability with

and without the effect of climate change in the study

area and analyse the water resources trend in the part of

the basin towards 2100.

Figure 1. Sokoto-Rima River Basins in Nigeria

222 Abdullahi S. A. et al.: Assessment of Water Availability in the Sokoto Rima River Basin

2.2. Description of the Study Area

The study area is Sokoto-Rima River Basin located in the

North-Western region of Nigeria, the area is found between

latitude 10° 04‘ N and Longitude 3° - 8° 14‘ E. The area

covers a land area of approximately 131,600 km2 and shares

its borders with Niger Republic to the north, and covers

Sokoto, Kebbi, Zamfara and large part of Katsina States to

the East; it also borders Niger State to the South-east, and

Benin Republic to the west. The whole basin can be

described as Sudan and Sahel Savanna, and it extends

beyond the border to Niger republic and the northern part of

Benin Republic. The basin topography consists of a vast

floodplain (fadama land) and rich alluvial soils that is

suitable for the cultivation of different variety of crops.

There are also isolated hills (inselberg) and hill ranges

scattered all over the area (Ekpoh and Ekpenyong, 2011).

2.3. Physical Features of the Study Area

The Sokoto basin falls within the hottest parts of Nigeria.

The critical zone, located above latitude 10°N, belongs to

the Sahel region of Africa, an area most affected by the

droughts. Temperatures are generally extreme, with average

daily minimum of 16℃ during cool months of January and

December, and in the hottest month of April to June, an

average maximum of 38 ℃ and minimum of 24 ℃ .

Throughout the year the average maximum is 36℃ and

average daily minimum is 21℃. Rainfall is generally low.

The average annual rainfall for 35 years is about 470mm.

Much of the rain falls between the month of may to

September, while the rainless months are October to April.

Evaporation is high ranging from 80mm in July to about

210mm in April to May.

A monthly average evaporation range of about 140mm

represent 30% of monthly average precipitation into the

catchment. The hottest months of April to May are periods

of highest evaporation. Relative humidity is low most of the

year and only increases during the wet seasons of June to

September. The vegetation is typically Sudan savannah and

is characterised by stunted and thorny shrubs, invariably of

the acacia species.

2.4. Description of Climate of the Basin

Like the rest of West Africa, the climate of the region is

controlled largely by the two dominant air masses affecting

the sub-region. These are the dry, dusty, tropical-

continental (cT) air mass (which originates from the Sahara

region), and the warm, tropical- maritime (mT) air mass

(which originates from the Atlantic Ocean). The influence

of both air masses on the region is determined largely by

the movement of the Inter-Tropical Convergence Zone

(ITCZ), a zone representing the surface demarcation

between the two air masses. The interplay of these two air

masses gives rise to two distinct seasons within the

sub-region. The wet season is associated with the tropical

maritime air mass, while the dry season is a product of the

tropical continental air mass. The influence and intensity of

the wet season decreases from the West African coast

northwards.

In terms of climatic statistics, the annual rainfall for

Sokoto ranges between 300 mm and 800 mm. The mean

annual temperature is 34.5 ℃ , although dry season

temperatures in the region often exceed 400C. (Ekpoh and

Ekponyong, 2011)

2.5. Description of Hydrology of the Basin

The basin is essentially drained by the river Sokoto, a

prominent part of Niger river drainage system. The sokoto

river rises with its main tributaries, the Ka, Zamfara, and

Rima from the 600 to 900 meters high Mashika and Dunia

highland areas bordering the eastern part of the basin, and

flows down, rather sluggishly down a gentle slope toward

the northwest, where around Sokoto town, it is joined by the

Rima in the north, making a southward swing, collecting

the Zamfara and Ka before entering in to the river Niger.

The river systems, thus effectively drains the whole basin.

At the source areas in the east, the Sokoto river system is

only seasonal. However in the western parts of the basin,

the river becomes perennial as it begins to receive

substantial ground water contribution to its flow.

2.6. Description of Land Use and Land Cover of the

Basin

The land use and land cover within the basin are grouped

in to five major categories: Settlements, Agricultural Land,

Vegetal Cover, Water Bodies and Bare and Rocky Surfaces.

Agricultural land is divided in to three categories: (a)

―Fadama‖, or land which historically has been seasonally

flooded or irrigated; (b) ―Tudu‖ , or land which lies above

the flood plain and is dependent on rainfall for its moisture;

and (c) land farmed by modern methods of irrigation for

example Talata-Mafara Irrigation scheme.

Table 1. Land Use and Land Cover of Sokoto-Rima River Basin

LAND USE IN SOKOTO RIMA RIVER BASIN

CATEGORY AREA IN km2

FOREST LAND/WOOD

LAND 2,755 2%

GRASS LAND 46,615 35%

AGRICULTURAL LAND 69,520 53%

WET LAND 970 0.74%

BARE LAND 10,330 7.85%

WATER AREA 1,400 1.06%

URBAN LAND 10 0.007%

GRAND TOTAL 131,600 100%

2.7. Description Demography of the Basin

In 1991, the population in the states of Katsina, Kebbi,

Sokoto, and Zamfara total to 10,291,799 people, and consists

of Urban and rural population. While the total population

according to 2006 census for those states total to 16,039,674


people, as shown in table 2 below. The whole states within

the basin have an average inter census growth rate of 3.11

and the vaerage population density of 130.35 in the year

2006.

2.8. Existing Water Infrastructure within the Basin

The two major dams in the Sokoto-Rima River Basin are

the Bakolori and Goronyo dams. The Bakolori Dam is in

Zamfara state, it was completed in 1978 and its reservoir

filled by 1981. It is a major reservoir on the Sokoto \River, a

tributary of the Rima River, which in turn feeds the River

Niger. Water from the dam supplies the Bakolori Irrigation

Project in TalataMafara. The dam has a capacity of 450

million cubic meters, with a reservoir covering 8,000

hectares extending 19 km (12 mi) upstream.

Table 2. Population Census of the states in Sokoto-Rima River Basin

STATES

CENSUS 1991

TOTAL

POPULATION

CENSUS 2006

TOTAL POPULATION

LAND SIZE

KM2

INTER

CENSUS

GROWTH

RATE

POPULATION

DENSITY

MALE FEMALE BOTH SEXES

KATSINA 3,753,133 2,948,279 2,853,305 5,801,584 24,971.22 3.04 232.3

KEBBI 2,068,490 1,631,629 1,624,912 3,256,541 37,727.97 3.17 86.3

SOKOTO 2,397,000 1,863,713 1,838,963 3,702,676 33,776.89 3.03 109.6

ZAMFARA 2,073,176 1,641,623 1,637,250 3,278,873 35,170.63 3.2 93.2

Table 3. Operation of the Goronyo and Bakolori Dams

Physical and Operations of the dam Goronyo dam Bakolori dam

Storage Capacity 942 Million m3 450 Million m3

Catchment Area 21445 Km2 4857 Km2

Active Capacity 933 Million m3 403 Million m3

Dead Capacity 9 Million m3 47 Million m3

Planned Irrgation Area

Operated Irrigation Area

69 000 Ha

17 000 Ha

23 000 Ha

23 000 Ha

Reservoir Area 200 Km2 80 Km2

Mean annual Inflow 656 Million m3 757 Million m3

Table 4. Existing Medium and Small Scale Irrigation Schemes within the Basin

EXISTING MEDIUM AND SMALL SCALE IRRIGATION

PROJECT RIVER WATER SOURCE WORKS IRRIGATION AREA (KM2)

GAGERE GAGERE WEIR 100

BAKURA LAKE NATU PUMP 50

KWARE RIMA PUMP 800

Table 5. Existing Large Scale Irrigation Schemes within the Basin

EXISTINGLARGE SCALE IRRIGATION

PROJECT RIVER WATER SOURCE WORKS IRRIGATION AREA (KM2)

BAKOLORI SOKOTO DAM 23000

WURNO RIMA DAM 1500

MIDDLE RIMA

VALLEY RIMA DAM 6500

ZAURO FOLDER RIMA DAM 13000


Goronyo Dam is on the River Rima at Goronyo in

Goronyo local government area of Sokoto state. It was

completed in 1984 and commissioned in 1992. The dam is a

sand-fill structure with a height of 21 m and a total length of

12.5 km. It has a storage capacity of 976 million cubic

meters. The dam is controlling floods and releasing water in

the dry season for the planned Zauro polder project

downstream in Kebbi state. Other large dams within the

basin are Gusau dam with height of 22m and total length of

800m located in Zamfara state and Zuru dam with height of

15m and total length of 700m located in Kebbi state. There

are also some small dams within the basin which include

Zurmi, Marina and Shagari dams.

3. Materials and Methods

3.1. Materials

The Materials used for this research are:

i. Hardware and software:- (a) The Hardware used is ―HP

Pavillion dv6‖ Laptop computer with window 7

installed as the operation system. (b) The softwares

used are GIS-ILWIS, WEAP and Microsoft Excel

(Microsoft Office Package).

ii. Large flow Current Meter for measurement of velocity

of flow in the river and determination of discharge, in

using it a thread was used to determine a straight cross

section line and divide the cross-section in to equal area

and a measuring tape was used for measuring distances.

iii. Internet used for research.

3.2. Methods

A water allocation modeling approach is adopted for this

study. First the model is applied to determine the surface

water resources availability for the current situation and

under the future changes of climate. Secondly, the model is

used to analyse the linkage between the water resources and

the demand in each region or local government based on the

population changes in the whole basin.

(a) Data collection as preliminary investigation and

analysis from the area was achieved by:

(i) Recognisance survey of the whole River Basin and

its surrounding Sub-Catchment areas.

(ii) Collecting the Hydrological and hydraulic data from

data stations in the area. The monthly average rainfall data,

the monthly average hydraulic data and the climatic data

which include Monthly average temperature for identified

major data stations in the sub-catchments for the period of

1970 – 2013 was obtained from the following data

stations:

(1) Birni-N'Konni, Niger, latitude: 13-48N, longitude:

005-15E, and elevation: 272m

(2) Gaya, Niger, latitude: 11-53N, longitude: 003-27E,

and elevation: 202 m

(3) Sokoto, Nigeria, latitude: 13-01N, longitude:

005-25E, and elevation: 302 m

(4) Gusau, Nigeria, latitude: 12-16N, longitude:

006-07E, and elevation: 469 m

(5) Yelwa, Nigeria, latitude: 10-88N, longitude:

004-75E, and elevation: 24 m and used for the

analysis, the locations are shown in the figure 4

below.

(b) GIS-ILWIS software was used to digitalize the

hydrologic map, land use map, and local government

administration map of the area and convert them to shape file

(i.e .shp file) that can be accepted by the WEAP software.

(c) Water demand for agriculture and consumption in each

subcatchment and the whole stretch of Sokoto Rima River

basin was obtained using population and the existing land

use and the hydrological characteristics of the catchment.

(d) The Modelling: The hydrological and hydraulic data

obtained and the parameters of a hydrological model in the

study area will be used in soil moisture method of Rainfall

runoff to generate current stream flows as the model of

available water in the area.

i.e Runoff = Precipitation - abstraction (1)

Hydrologic abstractions include interception, surface

storage, infiltration, and evapotranspiration. Climate is

assumed uniform over each sub-catchment, and the water

balance is given as:

Rdj

dz1,j

dt = Pe t – PET t kc,j t

5z1,j- 2z1,j2

3

– Pe t z1,j

RRFj- fjks,jz1,j

2 - 1- fj kz,jz1,j2 (2)

Where: z1,j = [1,0] is the relative storage given as a fraction

of the total effective storage of the root zone, 𝑅𝑑𝑗 (mm) for

land cover fraction, j, the effective precipitation, Pe,

excluding the snowmelt since snow is not experienced in the

study area.

Methods for Generating Climate Scenarios Adopted in

the Study:

Table 6. Hypothetical climate change scenarios

SCENARIOS

CHANGE IN

TEMPERATURE

ΔT (oC)

CHANGE IN

PRECIPITATION

P(mm)

REFERENCE 0 0

SCENARIO 1 + 0.5 0

SCENARIO 2 +0.5 +10%

SCENARIO 3 +0.5 -10%

SCENARIO 4 +1.0 0

SCENARIO 5 +1.0 +10%

SCENARIO 6 +1.0 -10%

The preferred methods in projecting future scenarios are

usually those derived from GCMs (GlobalClimatic Models)

but their limitations of grid-point predictions make them

very difficult to adapt to the regional analysis. Nevertheless,

use of hypothetical scenario is another option used by


researchers in climatic impact studies (Islam et.al., 2005).

Many published works were done in this way (e.g. Gleick,

1987; McCabe and Wolock, 1991; Skiles and Hanson, 1994;

Yates, 1996; Boorman and Sefton, 1997; Bobba, Jeffries and

Singh, 1999; Hailemariam, 1999; Xu, 1999, 2000; Islam,

Aramaki and Hanaki, 2005). From this perspective and

aiming to the main objective of the study to assess the

applicability of WEAP as a decision support system (DSS)

for climate impact assessment on a river basin, the

hypothetical scenario was chosen to generate scenarios. Six

hypothetical scenarios were adopted as follows, first

scenario consider a increase in temperature of about +0.5℃

over the entire basin, second scenario consider increase in

temperature of about +0.5℃ and an increase in precipitation

of around +10% over the entire basin, third scenario consider

increase in temperature of about +0.5℃ and decrease in

precipitation of around -10% over the entire basin, Fourth

scenario consider increase in temperature of about +1℃

over the entire basin, Fifth scenario consider increase in

temperature of about +1℃ and an increase in precipitation

of around +10% over the entire basin, while the sixth

scenario consider increase in temperature of about +1℃ and

decrease in precipitation of around -10% over the entire

basin.

2.3. Development of Weap Model

For the analyses of hydrological processes in the

sokoto-rima river basin, all natural hydrological watershed

details and infrastructure for water resources management

are represented in the WEAP model. The schematic

representation is shown in figure 2 below:

2.4. Analysis of Climate Change Impact on Water

Availability

The final stage is to quantify the water availability in all

scenarios from the simulation of the model. The water

availability within the catchments was evaluated based on

the following output of the WEAP model:

Total available water within the catchment under a

scenario – The total water demand within the catchment

The water availability in each scenarios then being

analysed in order to evaluate the sensitivity of the study area

to climate change based on the relation:

Percentage Impact

= Available remaining Water Under a given Scenario

Available Water from the observation actual data * 100% (3)

The impact of climate change on water demand and

supply can easily be analysed based on the availability of the

water within the basin.

Figure 2. The Schematic View of the Rivers in the Study Area


2.5. Water Year Method

The water year method is a means to represent variation in

climatic data like stream flow and rainfall. The method

involves defining how different climatic regime (e.g Very

Dry, Dry, Very Wet, Wet) compare relative to normal year,

which is given a value of one (1). Normal water year define

each non-Normal water year type (Very Dry, Dry, Wet, Very

Wet), specify how much more or less water flows into the

system in that year relative to a Normal water year. Dry years

have a value less than one (< 1), Very wet have a value

greater than one (> 1) For example, if a Wet year has 35%

more inflow than a Normal year, 1.35 will be entered for the

Wet year. These fractions are derived from a statistical

analysis of historical rainfall data obtained. First the years

are grouped into five bins (quintiles), then how they vary

from the norm are computed using the mean value of the

entire data as shown in the figure 3 below.

The Current Account year for this analysis happen to be a

normal water year. A single variation fraction is specified for

an entire water year type and for all the proposed scenarios.

The sensitivity to climate change was explored by

defining six scenarios. The reference scenario was adopted

using the Water Year Method to reproduce the observed

variation in hydrology from the historical record. The

remaining scenarios were adopted using the first as a starting

point, but altering each water year type according to

predicted effects of climate change (i.e., increase in

temperature and increase or decrease in Rainfall) as shown

below:

3. Results and Discussion

The six major rivers within the basin are delineated in the

WEAP as shown in figure 4 and 5 following their location on

the base map developed in GIS using the map of

North-Western region of Nigeria, the area is located between

latitude 10° 04‘ N and Longitude 3° - 8° 14‘ E.

The land use, present water abstractions and water

infrastructures were superimposed on the naturalised

hydrology in WEAP to simulate the basin‘s water resources.

The model simulation was assessed against observed stream

flow data for gauges located at some stations within the

basin.

Stream flow Simulation:

The data of 1970 to 1989 was used to set up the model and

validated with the streamflow data of 1970 to 2013. The

model was also calibrated with average coefficient of

determination (R2) of 0.04, and percentage error in total

runoff volume (VE) around 19% and percentage error in

peak discharge (PE) of around 17%. After calibration the

model was validated with the actual measurement of

streamflow at ten various points on the rivers within the

basin.

Based on the simulation and comparison of the sreamflow

within the basin for the reference scenario and scenarios 1 to

6, it was observed that the effect of the climate change is not

uniform. The difference in water availability from the

scenarios depends on the section of the stream observed. As

shown in figure 6 below, the difference in water volume

from the reference scenario to the worst scenario (scenario 6)

at river Bunsuru is not much but on reaching the river Rima

the difference is around 391 Billion Cubic Metres in 44 years

simulation, indicating a reduction of 8.9 Billion Cubic Metre

of water annually While the difference at river Sokoto is

1183 Billion Cubic Metres under the same period, indicating

a reduction of 26.9 Billion Cubic Metre of water from the

annual flow in that river, see figure 4 to 6 below.

Figure 3. Water Year Values


Figure 4. Streamflow for the basin

Figure 5. Streamflow below river sokoto for all scenarios

Figure 6. Streamflow at Bunsuru for Reference scenarios

Reference

SCENARIO 1

SCENARIO 2

SCENARIO 3

SCENARIO 4

SCENARIO 5

SCENARIO 6

S t r e a m f l o w ( b e l o w n o d e o r r e a c h l i s t e d )

R I V E R S O K O T O N o d e s a n d R e a c h e s : B e l o w R I V E R S O K O T O H e a d f l o w , A l l m o n t h s ( 1 2 ) , R i v e r : R I V E R S O K O T O

1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Billio

n C

ub

ic M

ete

r

10.0

9.5

9.0

8.5

8.0

7.5

7.0

6.5

6.0

5.5

5.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0


Streamflow for all seven rivers and their different nodes and reaches sections simulated for the period of 44 years are

shown in figure 7 below.

Figure 7. Streamflow for all scenarios

Figure 8. Streamflow for all scenarios Inflow and outflow

In summary, the model performance is good and reasonable when considering a larger part of the basin (figure 8). WEAP

offers a simplified representation of the complex workings of the basin hydrology by representing the actual conditions

within the basin using many ‗unknowns‘ and assumptions that are described in different sections of this work. The results of

water availability could be indirectly obtained from the model output.

In order to quantify how much is the water availability within the study area the average reservoirs storage volumes were

also determined as shown in figure 9.


Figure 9. Average monthly reservoir storage volumes

Monthly inflow and outflow from the two dams to downstream are also determined as shown in figure 10 below:

Figure 10. Reservoir inflow and outflow

The monthly average reservoir storage volume for all scenarios is shown in figure 11 below:

Figure 11. Average reservoir storage volume for all scenarios

Reference

SCENARIO 1

SCENARIO 2

SCENARIO 3

SCENARIO 4

SCENARIO 5

SCENARIO 6

R e s e r v o i r S t o r a g e V o l u m e

A l l R e s e r v o i r s ( 2 ) , M o n t h l y A v e r a g e

January February March April May June July August September October Nov ember December

Millio

n C

ub

ic M

ete

r

850

800

750

700

650

600

550

500

450

400

350

300

250

200

150

100

50

0


Table 7 shows the different amount of water availability based on the simulation due to different prescribed climate

scenarios. These indicate that under the worst scenario of increase in temperature by 1℃ and decrease in precipitation by

10% (i.e scenario 6) the minimum available water to the basin will be 4405.2 Million Cubic Meter.

Table 7. Effect of different climate scenarios to water availability based on the simulation of the sources for all rivers

AMOUNT OF WATER AVAILABLE IN (million) Cubic metre:

REFERENCE SCENARIO 1

+0.5OC

SCENARIO 2

+0.5OC, +10%P

SCENARIO

3+0.5OC,--10%P

SCENARIO

4+1.0OC,

SCENARIO 5

+1.0OC, +10%P

SCENARIO 6

+1.0OC,--10%P

Min 10958.9 10958.9 12545.1 4405.2 10958.9 12220.3 4405.2

Max 1324290.0 1319640.0 1554630.0 1037390.0 1315050.0 1532850.0 1030630.0

The inflow to areas for all scenarios and all month for 44 years simulated is shown in figure 12 below.

Figure 12. Inflow water volume for all scenarios

The Future Hydrology

Figure 13. Streamflow from rivers for all scenarios projected to 2064

RIVER BUNSURU 0 \ Headflow

RIVER BUNSURU 1 \ Withdrawal Node 11

RIVER BUNSURU 2 \ Reach

RIVER BUNSURU 3 \ Catchment Inflow Node 1

RIVER BUNSURU 4 \ Reach

RIVER GAGERE 0 \ Headflow

RIVER GAGERE 1 \ Withdrawal Node 10

RIVER GAGERE 2 \ Reach

RIVER GAGERE 3 \ Catchment Inflow Node 2

RIVER GAGERE 4 \ Reach

RIVER KA 0 \ Headflow

RIVER KA 1 \ Catchment Inflow Node 5

RIVER KA 2 \ Reach

RIVER KA 3 \ Withdrawal Node 7

RIVER KA 4 \ Reach

RIVER RIMA 0 \ Headflow

RIVER RIMA 1 \ RIVER BUNSURU Inflow

RIVER RIMA 2 \ Reach

RIVER RIMA 3 \ RIVER GAGERE Inflow


RIVER RIMA 5 \ Catchment Inflow Node 6


RIVER RIMA 7 \ Withdrawal Node 2


RIVER RIMA 9 \ GORONYO DAM






RIVER SOKOTO 0 \ Headflow

Streamflow (below node or reach listed)

All Years (95), All months (12), All Rivers (7)

Reference SCENARIO 1 SCENARIO 2 SCENARIO 3 SCENARIO 4 SCENARIO 5 SCENARIO 6

Bil

lio

n C

ub

ic M

ete

r

3,400

3,200

3,000

2,800

2,600

2,400

2,200

2,000

1,800

1,600

1,400

1,200

1,000

800

600

400

200

0


The impact of climate change on future availability of surface water to meet the demand obligations was assessed for the

Sokoto-Rima river basin using the seven scenario based climate dataset. Taking into consideration the model errors, the

results indicate higher future stream flows for the scenario 3 and 5. The magnitude of peak maximum monthly stream flow

increases by 17% relative to observed maximum monthly stream flow (year 1970 – 2013) as shown in figure 13 and 14.

The existing storage infrastructure will be able to buffer the deficits in meeting water demand in the basin based on the

reliability of the demand sites shown in figure 15.

The major domestic water demand from the basin is satisfied together with industrial requirements up to the year 2030.

However, demands for some smaller towns namely Sokoto North, Gusau and Goronyo are not met during the dry seasons.

Some of these towns will depend on alternative sources of water like groundwater. The model set up only assigned the

respective demands to rivers and alternative water supplies to towns was not considered. Therefore, the deficits in these towns

were assumed to be met from alternative sources like groundwater and considered insignificant. On the other hand, irrigation

demands constantly experience deficits during the dry season in the range of 10 – 13% in some river reaches.

Figure 14. Streamflow from rivers for all scenarios compared with reference scenario projected to 2064

Figure 15. Demand sites Reliability for all scenarios

Reference

SCENARIO 1

SCENARIO 2

SCENARIO 3

SCENARIO 4

SCENARIO 5

SCENARIO 6

D e m a n d S i t e R e l i a b i l i t y ( f o r e a c h D e m a n d S i t e )

ARGUNGU BIRNIN KEBBI GORONYO RIVER GAGERE CATCHMENT RIVER RIMA CATCHMENT RIVER ZAMFARA CATCHMENT SOKOTO NORTH

Perc

en

t

100

95

90

85

80

75

70

65

60

55

50

45

40

35

30

25

20

15

10

5

0


4. Conclusions and Recommendations

4.1. Conclusions

A model of the Sokoto-Rima River Basin was successfully

set up and a scenario analysis carried out under possible

impact of climate change. However, despite the quality of

checked and justified assumptions made on the data used,

errors would be inherent. Therefore, the results of this Study

should be viewed with caution at this stage. Nonetheless, the

results indicate an annual reduction in the total available

water of about 1.70 billion cubic metre and monthly water

demand of 17.11 Billion Cubic Meter for the month of April

(which is the driest month in the whole basin) selected sites

under 10% reduction in the actual rainfall within the basin

and increase in evapotranspiration under 1oC increase in

temperature, this indicate reduction of the surface water in

the future for the basin. In addition, the dependency of the

basin on surface water sources make it imperative to apply

some methods of efficient use of water resources in the basin

to ensure future sustainability.

This Study has initiated setting up of a model for the basin

which encompasses hydrology and some aspects of water

management on a single platform. It also presents the strong

ability of WEAP in modelling complex water systems thus

providing an opportunity for rapid assessment of the state of

existing water resources via scenario analyses.

4.2. Recommendations

The potential adaptation measures recommended for the

Sokoto Rima river basin to conserve its surface water supply

and minimize the investigated trend of surface water flow

based on this research are as follows:

1. Increase in water use efficiency and storage by using

new improved method of irrigation.

2. Using new improved varieties of different crops species

that does not require plenty of water in their production

by the farmers within the basin, to reduce

evapotranspiration.

3. Increasing the forested area and reducing the

impervious area by planting more trees to help in

percolating more water in to the soil an entrapping it.

4. Making a proper plan for the existing reservoirs to

maintain adequate flow in to downstream throughout

the year.

5. Creating more underground storage facilities (i,e

underground reservoirs).

6. Collaborative planning in using the surface water

among the stakeholders within the basin.

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Assessment of Water Availability in the Sokoto Rima River ...article.sapub.org/pdf/10.5923.j.re.20140405.03.pdf · Resources and Environment 2014, 4(5): 220-233 DOI: 10.5923/j.re.20140405.03